Coating finishing has hitherto been performed to protect a substrate of building structures, or civil engineering structures, and to impart design and to improve the appearance. However, a large amount of oily contaminants have recently been floating in the air as a result of an exhaust gas discharged from automobiles in the center of the city and suburbs thereof. When those oily contaminants adhere to the surface of the coat formed by using a high-durability coating, a considerable sooty or striped contamination (hereinafter referred to as "rain-striped contamination") occurs, therefore, the coating finishing provided to improve the scene of the city was meaningless sometimes.
Japanese Patent Kokai Publication No. 4-370176 discloses a coating comprising a segmented polymer containing a hydrophilic segment such as polyalkylene oxide segment and a hydrophobic segment such as polysiloxane. This coating is capable of obtaining such an effect that water derived from rainfall penetrates/flows into the interface between the coat and contaminants to wash off contaminants together with water (soil release effect) by imparting the hydrophilicity to the coat surface. Although the hydrophilicity is imparted when water is present on the coat surface, the hydrophobicity is actually imparted when the coat surface has no opportunity to contact with water for a long period of time. Therefore, there is a problem that it takes a considerably long time to convert the hydrophobicity of the coat surface into the hydrophilicity during rainfall , so that the contamination during rainfall can not be prevented.
Japanese Patent Application No. 6-506632 (International Publication WO94/06870) discloses an anti-contamination coating composition wherein organosilicate is added in the coating and the coat surface is bydrophilized by the reaction thereof and, furthermore, a soil release effect is utilized. The organosilicate forms a silanol group or a siloxane bond by the hydrolysis reaction in the presence of an acid catalyst, and these silanol groups or siloxane bond impart the hydrophilicity to the coat surface. Taking actual coating on the outside wall of buildings into consideration, the reaction may proceed by acidic rain, but it takes a considerably long period of time after formation of the coat to obtain the hydrophilic surface enough to sufficiently exert the soil release effect, similar to the above technique.
Japanese Patent Kokai Publication No. 6-145453 discloses a method of mixing an acrylic silicone resin with organosilicate to obtain a hydrophilic coat. According to this technique, a large amount of organosilicate is required to impart sufficient hydrophilicity to the coat. However, when a large amount of organosilicate is added, the crosslink density of the coat becomes too large and the coat becomes brittle. At the same time, a large amount of siloxane bonds are introduced to cause deterioration of the chemical resistance of the coat, which results in deterioration of the weathering resistance of the coat as contradiction.
In such a way, among coats formed by using conventional anti-contamination coating, those requiring a long period of time to hydrophilize the surface can cause rain-striped contamination within a very short period of time after application of the coating.
Originally, the anti-contamination coating has the effect of causing no contamination, and users and builders who request the coating expect that effect. Accordingly, the fact that contamination arises even at the initial stage after formation of the coat fails to meet the expectation of these users and builder temporarily, and the fact also imparts a sense of unease to the anti-contamination effect for a long period of time. Since a conventional anti-contamination coating has a main object of washing out contaminants by rainfall, the anti-contamination coating is inferior in stain resistance of once adhered contamination. It has been found that, when there is no rainfall for a long period of time, oily contamination penetrates into the coat to cause contamination which is hardly washed out by rainfall no longer.
An object to be solved by the present invention is to obtain an anti-contamination coating composition for providing an anti-contamination coat, which has a soil release effect of washing out contaminants because the surface exerts the hydrophilicity immediately after formation of the coat, not showing hydrophilicity by an action formed after formation of the coat, such as waterfall, and which is strong but not brittle because of its specific crosslinked structure, and has excellent stain resistance to oily contamination, good weathering resistance and good coat physical properties.
Another object to be solved by the present invention is to provide a coating composition, which can improve the interlaminar adhesion (hereinafter referred to as a "recoating property") when multi-layer coating is performed on a topcoat layer after curing an undercoat layer using a reaction curing type polyurethane or polyurethane-acrylic anti-contamination coating, and effectively prevent blister, crack or lifting (phenomenon wherein shrinkage occurs on the coat surface as a result of dissolution of the uncured portion of the undercoat layer by a solvent of the coating of the topcoat layer because of insufficient curing and adhesion of the coat of the undercoat layer in case of multiple coating) caused with a lapse of time.
Such an anti-contamination high-durability coating is exclusively a solution type of an organic solvent. With recent enhancement of the environmental awareness, there have been used those using as weak a solvent as possible. Furthermore, it has been required to convert into an aqueous coating.
It is generally considered that, when organosilicate (i.e. alkyl silicate) is added in the coating, it reacts with water in the air during the formation of the coat, and an alkoxysilyl group Si--OR is converted into a silanol group Si--OH and alkyl silicates having a silanol group are arranged on the coat surface, thereby exhibiting the hydrophilicity.
It is assumed that, when using a resin which is only dissolved in a solvent having high dissolving power, since the coat is certainly hydrophilic and the anti-contamination effect can also be obtained, such a surface orientation occurs. When using a urethane resin using a polyol having a solubility parameter of about 6.5 to 9.5, which is also dissolved or dispersed in a solvent having low dissolving power, there arise white turbidity of a film and such phenomenon that the anti-contamination is not obtained. Therefore, there is much room for improvement.
A finishing coating material whose main material layer has rubber elasticity referred to as a waterproofing multi-layer coating material, which is used in coating finishing performed in case of a substrate of building structures, civil engineering structures, etc., has been taken notice and widely used because it has a follow-up property to crazing (hereinafter referred to as "crack") of the outside wall of concrete and an effect for inhibition of penetration of a carbon dioxide gas.
This waterproofing multi-layer coating material is composed of an undercoat layer, a main material (a continuous layer and a patterned layer, which have rubber elasticity) and a topcoat material, but the topcoat layer is coated with an elastic coating following the main material layer. When coating finishing is performed on the whole outside wall including the butt portion (joint portion) between boards joined by using a sealing material in a dry technique using a dry building material represented by sideboard, extruded plate, etc., an elastic coating capable of following movement of the sealing material driven portion is used. Furthermore, an elastic coating is often used to a raw material such as metal, wherein degree of expansion and shrinkage is comparatively large, and to a substrate whose structural movement is assumed.
However, there is a problem that the coat obtained from these elastic coatings is generally inferior in resistance to surface contamination to a rigid coat.
Under these circumstances, the present inventors have found that, by mixing a hydrophilic alkoxysilane compound containing an alkylene oxide chain with an acrylic silicone resin and an alkyl silicate (organosilicate), as described in Japanese Patent Kokai Publication No. 9-31401, hydrophlization is exhibited from the comparatively initial stage in the coat surface to be formed from the composition. However, there was much room for improvement in anti-contamination performance immediately after formation of the coat.
The alkyl silicate (organosilicate) used in a conventional anti-contamination coating is closely related to brittleness of the formed coat, depending on the amount and combination with the kind of the used resin. Therefore, there is a fear of causing crack in the coat. Furthermore, the alkyl silicate (organosilicate) is very expensive as a raw material for coating and, therefore, it was a large problem to coating makers in view of the raw material cost.
That is, the problems to be solved by the present invention are as follows.
(i) To obtain an anti-contamination coating composition for providing an anti-contamination coat, which has a soil release effect of washing out contaminants because the surface exerts the hydrophilicity immediately after formation of the coat, not showing hydrophilicity by an action formed after formation of the coat, such as rainfall, etc., and has excellent stain resistance to oily contamination, good weathering resistance and good coat physical properties. PA1 (ii) To provide a coating composition, which can improve the interlaminar adhesion (hereinafter referred to as a "recoating property") when multi-layer coating is performed, and effectively prevent blister, crack or lifting caused with a lapse of time. PA1 (iii) To provide a coating composition, which has characteristics of the above items (i) and (ii), and can use a weak solvent which hardly causes environmental problems. PA1 (iv) To provide a coating composition, which has characteristics of the above items (i) and (ii), and forms an elastic coat which hardly causes crazing with a lapse of time. PA1 (v) To provide a coating composition, which exerts the same effect even if the amount of an expensive silicate compound mixed becomes lower in order to exhibit excellent soil-release effect immediately after formation of the coat, and also contributes to reduce the cost. PA1 (1) A composition which is mainly composed of a combination of a polyurethane-forming component (PU-I) and (C1). PA1 (2) A composition which is mainly composed of a combination of a polyurethane-forming component (PU-II) and (C2). This composition is characterized in that a weak solvent can be used, particularly. PA1 (3) A composition which is composed of a combination of a polyurethane-forming component (PU-III) and (C1) and polycaprolactone diol and/or polycaprolactone polyol as an essential component. This composition forms a coat having elasticity, particularly. PA1 (4) A composition which is mainly composed of a combination of an acrylic copolymer resin (AC) and (C1). PA1 (5) A composition which is mainly composed of a combination of an alkoxysilyl group-containing acrylic copolymer resin (AS) and (C1).